Imaging of the Brain and Spine
MRI is unparalleled in its ability to image the brain and spine.
In the brain, it is the test of choice in the diagnosis of stroke, brain cancer, multiple sclerosis, infection, and nearly every other possible condition affecting the brain. MRI can also provide detailed information about the blood supply to the brain (see below). Although imaging of the brain is often aided by the addition of intravenous contrast* material, most brain studies do not require this extra step.
In the spine, MRI offers exquisite detail about disc disease, arthritis, nerve root problems, tumors, and infection. For their patients with neck or low back pain, doctors often rely on MRI to diagnose pinched nerves and to help decide the best course of treatment. MRI also can help determine if pain is caused by something other than a pinched nerve. Even after surgery, MRI can be helpful in determining why pain recurs. Similar to brain studies, most imaging of the spine does not require the use of intravenous contrast.
Adequate blood supply is critical to the function of every organ in the body. Problems with blood supply can lead to a host of problems. Identifying those problems is often challenging.
The conventional method of imaging blood vessels is catheter angiography, in which a catheter is inserted into a large blood vessel using x-ray fluoroscopy; is then guided to the organ or region of interest under x-ray; and is then infused with intravenous contrast material while rapid, cinematic x-rays are obtained. The contrast outlines the inside of the blood vessels, and doctors analyze the x-ray images.
MRI can do all of this non-invasively and without the use of radiation. Special sequences designed to highlight flowing blood and suppress the signal from all other tissues allow exquisitely detailed computer reconstructions of even very small vessels. Nearly every vessel – from the largest in the body (the aorta) to the small vessels of the fingers and toes – can be seen, all without the use of radiation and often without the need for intravenous contrast.
This technology allows doctors to look for narrowing of blood vessels in the carotid arteries (which can increase the risk of stroke) or the kidneys (which can increase the risk of high blood pressure). It allows for the diagnosis of brain aneurysms before they rupture. It can also help determine if a patient with circulation problems would benefit from surgery or stent placement.
Most abdominal imaging is performed with CT or ultrasound.
Liver masses are relatively common entities and are frequently found while imaging is performed for something unrelated to the liver (a chest CT, for example, often includes many images of the liver; an ultrasound to check the kidneys or aorta may uncover a liver mass). Most liver masses are benign, but many are difficult to characterize with ultrasound or CT.
MRI has become the standard means by which to evaluate the liver. MRI is so accurate in liver imaging, in fact, that often times it will preclude the need for biopsy of masses seen in the liver. For patients with cirrhosis or hepatitis B or C, MRI is the best way to monitor for the development of liver cancer. However, in order for MRI to be accurate in liver cases, the use of intravenous contrast* is necessary.
Evaluation of the biliary system by MRI is now the standard of care. It does not require the administration of intravenous contrast and can create three-dimensional images of the biliary tree.
MRI is also extremely accurate in the diagnosis of pancreatic and kidney abnormalities. Often times in these cases, complementary imaging by CT and/or ultrasound can help clinch the diagnosis.
Advances in MR imaging now allow us to perform accurate imaging of the small and large bowel as well, something that until recently could only be done well by CT. Although CT remains the workhorse in this area, MR enterography is quickly gaining favor as a means of diagnosis for patients with inflammatory bowel disease, especially Crohn disease.
Crohn disease often affects younger individuals who then go on to require multiple imaging studies as the disease progresses and regresses. Concern over the cumulative radiation dose administered to these patients over time by the repeated use of CT has led doctors to seek alternative imaging methods. MR enterography not only provides exquisite detail about the bowel, it does so without any radiation (although intravenous contrast* is required). MR enterography has also supplanted x-ray small-bowel follow-through (SBFT) for the same reasons.
Finally in the abdomen, MRI is the test of choice in characterizing most adrenal masses. Like liver masses, adrenal masses are often found incidentally while imaging is done for something unrelated to the adrenals. Most adrenal masses are benign and are due to non-functioning adrenal adenomas. MRI can usually confirm the diagnosis without the need for intravenous contrast.
In most cases, ultrasound is the best test to assess pelvic abnormalities. But in some cases, ultrasound cannot distinguish between benign and malignant masses, especially in the ovaries. MRI is often very useful in helping narrow the diagnosis of ovarian disease.
In patients with cervical cancer, MRI serves as the best way to measure extent of disease and ensure that the patient is a good candidate for surgery. Similarly, MRI provides useful information for both the surgeon and the radiation oncologist in patients with prostate cancer by helping outline exactly where the tumor is in relation to nearby structures, including the nerves near the prostate.
Muscles, Joints, and Bones
MRI is the gold standard for the evaluation of all musculoskeletal disease, from knees to shoulders and fingers to toes.
Plain x-rays are often helpful complementary images to MRI. Ultrasound has become very useful in evaluation of many disease processes that are relatively near the skin, such as the Achilles tendon or the flexor and extensor tendons of the fingers.
But nothing beats the ability of MRI assess all of the ligaments, tendons, muscles, and joint spaces in the body. MRI is the best way to look at cartilage and provides invaluable information about bony diseases. From fractures to tumors and even for evaluation after surgery, MRI does it all, usually without the need for intravenous contrast administration.
One traditional weakness in MRI imaging of the musculoskeletal system has been its inability to image patients who have surgically implanted metal, such as total knee or hip replacements or spinal hardware. Thanks to developing new technology which allows for metal artifact suppression, MRI will be able to offer its unparalleled imaging power to post-operative patients as well.
* Patients with certain medical conditions may not be suitable candidates for intravenous contrast administration. See “Preparation.”